ROSSIER Daniel wrote:
> Hi all,
>
> I've found a bug in arch/arm/xenomai/switch.S which solved the problem below.
> It actually comes from the iWMMXT (Intel Wireless MMX) coprocessor which is
> an extension of the ARM core in Xscale processor (and of course which is not
> available in the AT91 series ;-).
>
> When a thread switch occurs, rthal_thread_switch(in
> arch/arm/xenomai/switch.S) is called to perform switching of registers and
> stacks between threads. The PXA version must also perform a switch of MMX
> registers by invoking iwmmxt_task_switch(in arch/arm/kernel/iwmmxt.S). This
> is done in rthal_task_switch() as well.
>
> However, between Linux 2.6.15 and Linux 2.6.20, the general scheme of
> low-level task switching procedure changed a little bit: it is now relying on
> a call chain notifier-based mechanism. Therefore, the iwmmxt_task_switch()
> function has been updated since the function is called now from the notifier,
> and not directly from __switch_to() as in 2.6.15. And the ipipe (ARM) patch
> did not take into account that.. and it fails.
>
> So, as a first workaround, I simply duplicated the iwmmxt_task_switch()
> function making the version (from 2.6.15) proprietary to ipipe by renaming to
> iwmmxt_task_switch_from_ipipe(), and modified arch/arm/xenomai/switch.S
> accordingly (be careful, switch.S is a symlink and actually belongs to
> Xenomai tree (ksrc/arch/arm).
>
> It seems to work so far, but further tests are needed (and will be done).
>
> I attached a patch to be applied in the (xenomai-patched) Linux tree.
> (Linux 2.6.20, xenomai from today svn).
>
Task switching is not I-pipe's business, and we should refrain from
recycling code from older kernel versions into recent ones. AFAICS, we
only need to conform to some new internal API. Food for thought below:
--- ksrc/arch/arm/switch.S (revision 3095)
+++ ksrc/arch/arm/switch.S (working copy)
@@ -18,6 +18,7 @@
*/
#include <linux/linkage.h>
+#include <linux/version.h>
#include <asm/assembler.h>
#include <asm/asm-offsets.h>
@@ -86,7 +87,13 @@
VFPFMXR FPEXC, r4
#endif
#if defined(CONFIG_IWMMXT)
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,18)
+ mr r0, r2
bl iwmmxt_task_switch
+ mr r2, r0
+#else
+ bl iwmmxt_task_switch
+#endif
#elif defined(CONFIG_CPU_XSCALE)
add r4, r2, #40 @ cpu_context_save->extra
ldmib r4, {r4, r5}
--
Philippe.
_______________________________________________
Xenomai-core mailing list
[email protected]
https://mail.gna.org/listinfo/xenomai-core
